[qt] refactor: qt_common lib (#94)

This is part of a series of PRs made in preparation for the QML rewrite. this PR specifically moves a bunch of utility functions from main.cpp into qt_common, with the biggest benefit being that QML can reuse the exact same code through ctx passthrough.

Also, QtCommon::Frontend is an abstraction layer over several previously Widgets-specific stuff like QMessageBox that gets used everywhere. The idea is that once QML is implemented, these functions can have a Quick version implemented for systems that don't work well with Widgets (sun) or for those on Plasma 6+ (reduces memory usage w/o Widgets linkage) although Quick from C++ is actually anal, but whatever.

Other than that this should also just kinda reduce the size of main.cpp which is a 6000-line behemoth rn, and clangd straight up gives up with it for me (likely caused by the massive amount of headers, which this DOES reduce).

In the future, I probably want to create a common strings lookup table that both Qt and QML can reference--though I'm not sure how much linguist likes that--which should give us a way to keep language consistent (use frozen-map).

TODO: Docs for Qt stuff

Co-authored-by: MaranBr <maranbr@outlook.com>
Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/94
Reviewed-by: MaranBr <maranbr@eden-emu.dev>
Reviewed-by: Shinmegumi <shinmegumi@eden-emu.dev>

src/android/app/src/main/res/values-ja/strings.xml

@@ -491,8 +491,6 @@
     <string name="use_custom_rtc">カスタム RTC</string>
     <string name="use_custom_rtc_description">現在のシステム時間とは別に、任意のリアルタイムクロックを設定できます。</string>
     <string name="set_custom_rtc">カスタムRTCを設定</string>
-    <string name="disable_nca_verification">NCA検証を無効化</string>
-    <string name="disable_nca_verification_description">NCAコンテンツアーカイブの整合性検証を無効にします。読み込み速度が向上する可能性がありますが、データ破損や不正なファイルが検出されないリスクがあります。ファームウェア20以上が必要なゲームや更新を動作させるために必要です。</string>
 
     <!-- Network settings strings -->
     <string name="generate">生成</string>